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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package network
import (
"context"
"fmt"
"net"
"github.com/algorand/go-algorand/logging"
)
func readFromSRV(service string, protocol string, name string, fallbackDNSResolverAddress string, secure bool) (records []*net.SRV, err error) {
log := logging.Base()
if name == "" {
log.Debug("no dns lookup due to empty name")
return
}
if protocol != "tcp" && protocol != "udp" && protocol != "tls" {
err = fmt.Errorf("unsupported protocol '%s' specified", protocol)
return
}
controller := NewResolveController(secure, fallbackDNSResolverAddress, log)
systemResolver := controller.SystemResolver()
_, records, sysLookupErr := systemResolver.LookupSRV(context.Background(), service, protocol, name)
if sysLookupErr != nil {
log.Infof("ReadFromBootstrap: DNS LookupSRV failed when using system resolver: %v", sysLookupErr)
var fallbackLookupErr error
if fallbackDNSResolverAddress != "" {
fallbackResolver := controller.FallbackResolver()
_, records, fallbackLookupErr = fallbackResolver.LookupSRV(context.Background(), service, protocol, name)
}
if fallbackLookupErr != nil {
log.Infof("ReadFromBootstrap: DNS LookupSRV failed when using fallback '%s' resolver: %v", fallbackDNSResolverAddress, fallbackLookupErr)
}
if fallbackLookupErr != nil || fallbackDNSResolverAddress == "" {
fallbackResolver := controller.DefaultResolver()
var defaultLookupErr error
_, records, defaultLookupErr = fallbackResolver.LookupSRV(context.Background(), service, protocol, name)
if defaultLookupErr != nil {
err = fmt.Errorf("ReadFromBootstrap: DNS LookupSRV failed when using system resolver(%v), fallback resolver(%v), as well as using default resolver due to %v", sysLookupErr, fallbackLookupErr, defaultLookupErr)
return
}
}
}
return records, err
}
// ReadFromSRV is a helper to collect SRV addresses for a given name
func ReadFromSRV(service string, protocol string, name string, fallbackDNSResolverAddress string, secure bool) (addrs []string, err error) {
records, err := readFromSRV(service, protocol, name, fallbackDNSResolverAddress, secure)
if err != nil {
return addrs, err
}
for _, srv := range records {
// empty target won't take us far; skip these
if srv.Target == "" {
continue
}
// according to the SRV spec, each target need to end with a dot. While this would make a valid host name, including the
// last dot could lead to a non-canonical domain name representation, which is better avoided.
if srv.Target[len(srv.Target)-1:] == "." {
srv.Target = srv.Target[:len(srv.Target)-1]
}
addrs = append(addrs, fmt.Sprintf("%s:%d", srv.Target, srv.Port))
}
return
}
// ReadFromSRVPriority is a helper to collect SRV addresses with priorities for a given name
func ReadFromSRVPriority(service string, protocol string, name string, fallbackDNSResolverAddress string, secure bool) (prioAddrs map[uint16][]string, err error) {
records, err := readFromSRV(service, protocol, name, fallbackDNSResolverAddress, secure)
if err != nil {
return prioAddrs, err
}
prioAddrs = make(map[uint16][]string, 4)
for _, srv := range records {
// empty target won't take us far; skip these
if srv.Target == "" {
continue
}
// according to the SRV spec, each target need to end with a dot. While this would make a valid host name, including the
// last dot could lead to a non-canonical domain name representation, which would better get avoided.
if srv.Target[len(srv.Target)-1:] == "." {
srv.Target = srv.Target[:len(srv.Target)-1]
}
addrs := prioAddrs[srv.Priority]
addrs = append(addrs, fmt.Sprintf("%s:%d", srv.Target, srv.Port))
prioAddrs[srv.Priority] = addrs
}
return
}
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